Electromagnetic door locks are widely used in diverse electronic door applications. These locks typically use electromagnets attached to the door frame in conjunction with a ferromagnetic strike plate attached to the door, to hold the door firmly closed.
In many current designs, means are provided in the electromagnetic door lock to permit a controlled amount of door movement in the opening direction while the armature or strike plate of the lock remains in contact with an energized electromagnet, to improve the ability of a door equipped with a magnetic lock to withstand a physical blow. A coil spring disposed with the door allows for some relative movement between the door and strike plate. This design feature of the electromagnetic strike is referred to herein as an “Energy Absorbing” design feature. The means provides linear elasticity to the door by absorbing some of the kinetic energy of the blow upon compression of the spring, thus lowering the peak force experienced to separate the strike plate from the electromagnet during a physical attack against the door and allowing for a lower powered electromagnet to be used.
In current electromagnetic door lock designs, there may also exist a means that momentarily delays de-energizing of the electromagnet after a force to open the door is applied. This design feature is often associated with exit doors in commercial buildings or restaurants that permit emergency egress through doors normally locked. In a delayed magnetic lock (:“De-Mag” design feature), if an opening force is applied to a locked door continuously through a first predetermined period of time (the “delay period”), the electromagnet will be de-energized, allowing the door to be opened. If the opening force applied to the door is terminated within a second predetermined period of time (the “nuisance delay period”) wherein the second predetermined period of time is less than the first predetermined period of time, the electromagnet will remain energized and the door will remain locked. Typically, an audible signal will be sounded during the first predetermined period of time providing an alarm that an attempt is being made to exit through the locked door.
In current electromagnetic door lock designs, there may also exist a power savings design feature (Eco-Mag design feature). By the Eco-Mag design feature, the electromagnet has a resting state wherein only enough power is supplied to the electromagnet to keep the door in a locked state when subjected to only environmental stimuli such as a gust of wind. Then, should a more forceful attempt be made to open the door (i.e., an unauthorized attempt to enter), power to the electromagnet is increased to keep the door locked against the unauthorized attempt to open the door. The Eco-Mag design feature also requires a controlled amount of door movement in the door-opening direction, while the strike plate remains in contact with the energized electromagnet, in order for a door position sensor to sense when an unauthorized attempt to enter is being made.
In each of the three design features (Energy Absorbing, De-Mag or Eco-Mag), the electromagnetic door lock provides for a strike plate mounting bolt assembly whereby, while the strike plate remains in contact with an energized electromagnet, the door moves slightly away from the door frame when a force to open the door is applied to the door. In the prior art, the strike plate mounting bolt assembly includes a relatively large coil spring resiliently mounted in a through bore in the door to provide for relative movement between the door and strike plate. The prior art mounting bolt assembly required a large diameter hole to be bored through the door in order to receive the coil spring. Further, in the prior art, with the use of a coil spring as the resilient member, the dynamics of allowable door movement, that is, the door opening force and amount of door movement needed to compress the spring were not readily adjustable to accommodate the varied requirements of the above mentioned design features.
What is needed in the art is a strike plate mounting bolt assembly used in an electromagnetic door lock that provides for a more compact and robust electromagnetic door lock.
What is also needed in the art is a strike plate mounting bolt assembly used in an electromagnetic door lock that may be conveniently and selectively adjusted in the field to accommodate various needs of the associated electromagnetic door lock.
It is the principal object of the present invention to provide these and other needs.